Study On Ground Deformation And Risk Analysis In Shield Tunnel Of Tianjin Double-line Metro In Soft Soil Layer

The stratum deformation is unavoidable in the construction of Metro tunnel.If the stratum deformation is not controlled in time,it will cause serious consequences.Especially in the construction of double-line shield in soft soil stratum,the stratum deformation will be more complicated due to the interaction between the two lines.Tianjin soft soil stratum has the characteristics of large thickness and low bearing capacity.It is easy to produce uneven settlement during excavation,and it is difficult to construct subway tunnel.Therefore,how to effectively guarantee the safety of double-track tunnel construction in soft soil stratum has become the key point of engineering control.Based on the double-line shield tunneling project of Tianjin Metro Line 5 and 6,this paper focuses on the analysis of surface settlement law,dividing of influential portion,and risk assessment,and draws corresponding conclusions.In addition,this paper studies the construction process of the four-line overlapping tunnel of Tianjin Metro Line 5 and 6,and verifies the adaptability of the research conclusion in soft soil stratum,so as to provide reference for the design and construction of double-line shield tunnels in Tianjin in the future.The main research contents and results are as follows:(1)Based on the statistical analysis of plenty of measured data,this paper studies the law of ground subsidence in the actual construction process.Considering that the ground subsidence caused by the construction of double-track tunnel is the superposition of the ground subsidence caused by the first tunnel and the second tunnel,the two parameters of Peck formula,the stratum loss rate Vi and the width coefficient k of settlement trough,are used to predict the ground subsidence of double-track shield tunnel in soil layer.(2)The criteria for dividing the influential portion of tunnel construction in Tianjin soft soil stratum are determined.Taking the Xingfugongyuan Station-Jingjiang Road Station-Chenglin Road Station as the research object,according to the actual engineering geological conditions,the division of strong,weak and non-influence zones under the condition of comprehensive judgment criteria is determined by numerical simulation,and the reasonable spacing of overpass tunnels is studied.(3)A risk evaluation index system for double-track shield tunneling in Tianjin soft soil stratum is established,which includes six first-level factors,23 second-level factors,and five third-level factors.Simultaneously,a model of fuzzy analytic hierarchy process is established to visualize and quantify the results of risk assessment.(4)Based on the overlapping section of Tianjin Metro Line 5 and Line 6,the construction process,net distance between shield tunnels,and grouting effects are analyzed.By comparing the measured data,the method in this paper and the numerical simulation,the reliability of the law of surface subsidence,the influence zoning and the risk assessment method in the complex overlapping interval is verified.